Opel Automobile Owner's Manual page 211

Coolant and antifreeze
Use only silicate-free long life coolant
(LLC) antifreeze.
The system is factory filled with
coolant designed for excellent
corrosion protection and frost
protection down to approx. -28 °C.
This concentration should be
maintained all year round. The use of
additional coolant additives that
intend to give additional corrosion
protection or seal against minor leaks
can cause function problems. Liability
for consequences resulting from the
use of additional coolant additives will
be rejected.
Brake and clutch fluid
Only use high-performance brake
fluid approved for the vehicle, consult
your workshop.
Over time, brake fluid absorbs
moisture which will reduce braking
effectiveness. The brake fluid should
therefore be replaced at the specified
interval.
Brake fluid should be stored in
a sealed container to avoid water
absorption.
Ensure brake fluid does not become
contaminated.
Service and maintenance 211